Topic 11b: Arthropods (Ízeltlábúak)

Arthropods represent 80% of all animals and exhibit amazing diversity.  They include centipedes, crabs, spiders and insects!

Body Structure
- protostomes
- bilateral symmetry
- coelomates

movement
- have jointed appendages (legs or antenna) (ízelt függelékek)

Various jointed appendages

- have exoskeletons made from protein and chitin (disadvantage of an external skeleton is that they have to moult (vedleni) to grow.  Most will moult 4 - 7 times in their lifetimes)

- some have a waxy layer covering their exoskeleton to reduce water loss
- skeletal muscles (vázizmok)


- segmentation:  centipedes show basic segmention, but most other arthropods have fused segments into 3 major body parts:  head, thorax (tor) and abdomen (potroh)

respiration
-  3 types of organs are found in this group:
insects have tracheal tubes (légcsőrendszer)


crustaceans have gills
spiders have book lungs

nervous system
- ganglionic nervous system:  small brain in the head and double ventral nerve cords with ganglia in each segment

- antennae are used to sense sounds (vibrations) or chemicals
- compound eyes have many lenses and are used to sense movement
- simple eyes have single lenses and are used to sense light

circulatory system
- open circulatory system:  blood is pumped from the heart into the spaces around the organs

nutrition
- a simple digestive system (mouth, stomach, intestines, anus), with glands (mirigyek) that produce digestive enzymes.
- mouthparts are highly variable, adapted to diet, eg. piercing mandibles, sucking tube, sponging tongue etc.

Various mouthparts

excretion
- have Malpighian tubules which collect up nitrogenous waste and empty into the intestines.

Origin/Evolution
- evolved from primitive annelids
- there has been a reduction of body segments through evolution
- segments have become more complex

Classification
We will cover 5 major classes.

1.  Centipedes
-live in moist places
- have long, flattened bodies (15-181 segments)
- 1 pair of legs/segment
- predators

2.  Millipedes
- have long cylindrical bodies
- 2 pairs of legs/segment (segement fusion)
- eat plants or dead material

3.  Crustaceans (crabs, crayfish, shrimp. lobster)

Red crab

Mud crab

Crayfish

Lobster

Snowball shrimp

Pedersen's shrimp

- aquatic with gills
- head has mandibles, 2 pairs of antennae, 2 compound eyes
- 5 pairs of jointed legs (used for walking), the 1st pair is specialized for seizing prey (called pincers)
- swimmerets (potrohlábak) are attached to the abdoment, useful for making water flow over the gills, crayfish, shrimp and lobsters have 5 pairs
- most have 3 body segments, some have 2 (eg. crayfish), where the cephalothorax is covered by the carapace (rákpáncél)

-exoskeleton also contains calcareous salts
- unusual examples of crustaceans include barnacles (tengeri makk), water fleas (vizibolha) and pill bugs (gombászka)

Barnacles

Water flea

Pill bug

4.  Arachinids - spiders, scorpions, mites (atka) and ticks (kullancs)

Scorpion

Cheese mites

Dust mite

Tick

Spiders

Garden spider

- more than 30 000 species of spiders on the planet
- terrestrial, book lung
- segmentation: cephalothorax is called the prosoma and the abdomen is called the opisthosoma

- no antennae
- no compound eyes, 6-8 simple eyes (detect light)

Wolf spider

- jointed appendages include:
chelicerae (csáprágok) near the mouth (hold food, inject poison)
pedipalps (tapogatóláb) handle food, sense and in males carry sperm
4 pairs of walking legs

- spin silk from their silk gland (szövőmirigy) found on the opisthosoma with help of spinnerets (szövőszemölcs) - silk is for egg sacs and webs (not all make webs)

Spider egg sac

Spider egg sac

5.  Insects (rovarok)
- over 800 000 known species
- found everywhere
- very diverse
- 3 body parts:
head - antennae, 2 compound eyes, several simple eyes, mouthparts

Simplified insect body structure

thorax - made from 3 fused segments, therefore 3 pairs of legs, also has 2 pairs of wings (usually, but flies and mosquitos only have one pair and in beetles the 1st pair is hardened into an outer carapace)

House fly

Potato beetle

Ladybird (or ladybug)

abdomen - segmented, each segment has a pari of lateral pores called spiracles (légnyilások) for air to enter the tracheal tubes (légcsőrendszer)
- reproduction is sexual, insects lay eggs from which larval stages hatch and as they grow they go through metamorphosis (átalakulás)

Complete metamorphosis

Butterflies are a good example of complete metamorphosis (the juvenile forms look completely different from the adult)

Gradual/ Incomplete metamorphosis

Grasshoppers are a good example of an insect that has gradual metamorphosis (young look very much like the adult)

Asexual reproduction can occur:

parthenogenesis (szűznemzés) is the development of unfertilized eggs, for example this is seen in honeybees, where the males (drones) hatch from unfertilized eggs.

another example of this can be seen in the case of aphids (levéltetű), where if conditions are favourable the female births many female clones (no eggs involved), in bad conditions, winged females mate with males to produce fertilized eggs.

Female aphid giving live birth to a small clone of itself!